All numerical controlled (NC) lathes are equipped with different tools for the various machining operations and require either that a new tool be indexed forwardly in the tool revolver or be collected from a tool magazine connected to the lathe. The time for tool change varies greatly depending on the size of the machine, but lies as rule between 1 and 10 seconds. The cutting of complicated details with short times of machining and at high number of revolutions, causes many tools to be used and the unproductive time of the machine becomes long. For some jobs, values of more than 50% are mentioned regarding unproductive time.
Machine development has brought about the provision of a milling spindle to the modern NC lath in the x direction but which in principle can move freely in the working area and can reach the work piece from all directions in machines with multi-functions with a so called B spindle. The problem lies nowadays in that tools are not optimized for use in the new machines.
British Patent 2,122,124 shows a cutting tool provided with a shank connected to a head. The head carries three axially directed cutting edges, which are indexed to the active position as the preceding cutting edge becomes worn out.